Actually crypto is a dangerous place for investment if you did not buy suitable coin for future hold. No doubt that BTC hold is always batter but not all altcoins. I think altcoins have to be hold though roadmap and team activities otherwise it would be lose project all time.
Actually every investment has risk because there's no assurance to gain from it. Crypto is not different especially if you decided to invest because of hype. This is often the problem of those who engage themselves without interest to dig deeper on how it really works to become knowledgeable.
Recently there are many projects who rug pulled resulting for many investors to lose their money. Investing in these coins are quite risky especially if you're greedy not to sell even the price is decent enough to take profit. Alts are ideal for short term but if your plan is to hold for long period then the best choice is Bitcoin. However, op is right to know when to sell and buy back during dip. It can maximize your profit but it requires an effective strategy and its a must that you know what you're doing.